The invention generally relates to methods and devices for detecting, quantifying and analyzing light, as well as for imaging.
‘Light’ is a form of radiant energy, an electromagnetic radiation whose wavelength is between approximately 100 and 0.01 μm. Visible light has a wavelength between approximately 0.4 to 0.76 μm.
Conventional light sensors include transduction elements that convert electromagnetic radiation into a usable electrical output. Four transduction principles are commonly used: photovoltaic, photoconductive, photoconductive junction, and photoemissive. Modern light sensors incorporate transduction elements that are semiconductor-based.
Quantum efficiency (QE) is the ratio of countable output events to the number of incident photons and is used to gauge the relative performance of transduction elements. For transduction elements, a countable event is generation of an electron in response to a single incident photon. Thus, if one incident photon generates one measurable electron the QE is 100%. Semiconductor-based light sensors generally operate with a QE in the range of about 0.1% to about 35%.
The poor QE means that a photon sensor based on semi-conductors requires numerous photons to produce measurable electrons, thereby having reduced sensitivity.
Reduced sensitivity due to a low QE requires that a low-light imaging device based on semiconductors use enhancing techniques, such as infra-red strobe lights, to increase the number of photons to measure. These techniques add significantly to the cost and size of low-light imaging devices.
Producing an instrument to selectively measure a range of light frequencies (colors) using semiconductor transducers disadvantageously requires bulky, QE-reducing diffraction gratings. Thus, the already-inefficient photon sensor of such a device is further limited by loss of photons due to the diffraction grating.